Implantable permanent and temporary medical electrical stimulation and/or sensing leads are well known in the fields of cardiac stimulation and monitoring, including cardiac pacing and cardioversion/defibrillation, and in other fields of electrical stimulation or monitoring of electrical signals or other physiologic parameters. In the field of cardiac stimulation and monitoring, the electrodes of epicardial or endocardial cardiac leads are affixed to the myocardium of the heart wall through either the epicardium or the endocardium, respectively, bear against the epicardium or endocardium, respectively, or are lodged in a coronary vessel.
The lead body of a permanent or temporary cardiac lead typically includes one or more insulated conductive wires surrounded by an insulating outer sheath. Each conductive wire couples a proximal lead connector element with a distal stimulation and/or sensing electrode. Temporary and permanent cardiac leads having a single stimulation and/or sensing electrode at the lead distal end, a single conductor, and a single connector element are referred to as unipolar cardiac leads. Temporary and permanent cardiac leads having two or more stimulation and/or sensing electrodes at the lead distal end, two or more respective conductors, and two or more respective connector elements are referred to as bipolar leads or multi-polar leads, respectively.
Epicardial or myocardial permanent and temporary cardiac leads, or simply epicardial leads, are implanted by exposure of the epicardium of the heart typically through a limited thorocotomy or a more extensive surgical exposure made to perform other corrective procedures. Endocardial permanent and temporary cardiac leads, or simply endocardial leads, are implanted through a transvenous route to locate one or more sensing and/or stimulation electrode along or at the distal end of the lead in a desired implantation site in a chamber of the heart or a blood vessel of the heart. It is necessary to accurately position the electrode surface against the endocardium or within the myocardium or coronary vessel at the implantation site.
Temporary epicardial or endocardial cardiac leads are designed to extend through the patient's skin to an external monitor or pacing pulse generator to provide temporary pacing and to be removed from the patient's body when temporary pacing is halted. Permanent epicardial and endocardial cardiac leads are designed to be coupled to a pacemaker or defibrillator implantable pulse generator (IPG) or an implanted monitor and to be chronically implanted in the patient's body. The proximal end of such permanent cardiac leads typically is formed with one or more lead connector element that connects to a terminal of the IPG or monitor.
Referring particularly to the transvenous implantation of permanent endocardial leads, the distal electrode of the endocardial cardiac lead is advanced through the subclavian, jugular, or cephalic vein and through the superior vena cava into the right atrium or right ventricle or into a cardiac vessel, e.g., the coronary sinus and vessels branching therefrom, so as to locate the distal electrode(s) at a desired implantation site. Such a pathway involves a number of twists and turns and is relatively tortuous. An active or passive fixation mechanism is incorporated into the distal end of the permanent endocardial lead and is deployed at the implantation site to maintain the distal end electrode in contact with the endocardium or within the myocardium.
Considerable effort has been undertaken to develop passive and active fixation mechanisms that are simple to use and reliable in maintaining the distal electrodes in position. Passive fixation mechanisms do not invade the myocardium but cooperate with cardiac tissue or structures to lodge the pace/sense electrode(s) against the endocardium. The most successful passive fixation mechanism includes a plurality of soft, pliant tines that bear against cardiac structure surfaces, e.g. the trabeculae in the right ventricle and the atrial appendage, to urge the distal tip electrode against the endocardium without penetrating into the myocardium. Active fixation mechanisms are designed to penetrate the endocardial surface and lodge in the myocardium without perforating through the epicardium or into an adjoining chamber. The most widely used active fixation mechanism employs a sharpened helix, which typically also constitutes the distal tip electrode. Typically, some sort of shroud or retraction mechanism is provided to shield the helix during the transvenous advancement into the desired heart chamber from which the helix can be advanced and rotated when the desired implantation site is reached to effect a penetrating, screw-in fixation. In one manner or another, the helix is adapted to be rotated by some means from the proximal end of the lead body outside the patient's body in order to screw the helix into the myocardium and permanently fix the electrode.
More recently, endocardial pacing and cardioversion/defibrillation leads have been developed that are adapted to be advanced into the coronary sinus to locate the distal electrode(s) adjacent to the left atrium or into coronary veins branching from the coronary sinus to locate the distal electrode(s) adjacent to the left ventricle. The distal end of such a coronary sinus lead is advanced through the superior vena cava, the right atrium, the valve of the coronary sinus, the coronary sinus, and, if employed to pace or sense the left ventricle, into a cardiac vein branching from the coronary sinus. Typically, coronary sinus leads employ a form of passive fixation, e.g., a preformed shape of the distal segment of the lead that relies on the close confinement within the vessel and column stiffness to maintain each electrode at a desired implantation site.
The heart beats approximately 100,000 times per day or over 30 million times a year, and each beat stresses at least the distal end segment of an implanted permanent endocardial lead. The lead conductors and insulation are subjected to cumulative mechanical stresses, as well as material reactions, over the years of implantation that can result in degradation of the insulation or fractures of the lead conductors with untoward effects on device performance and patient well being. The endocardial lead body is subjected to continuous flexing as the heart contracts and relaxes and is formed to be highly supple, flexible and durable. Thus, the permanent endocardial lead body lacks the column stiffness necessary to push the lead body through the twists and turns of the venous pathway and into the desired implantation sites in a right heart chamber or within the coronary sinus or cardiac vein. Historically, it has been necessary to temporarily stiffen the lead body to advance the lead distal end through these blood vessels and to locate the distal electrode(s) at the desired implantation site.
Implantable endocardial bipolar cardiac pacing leads of the type first disclosed in U.S. Pat. No. 3,348,548 included separate coiled wire conductors in a side-by-side configuration providing a coil lumen for receiving a stiffening stylet. Side-by-side coiled wire conductors have largely been supplanted by a coaxial configuration of the type shown in U.S. Pat. No. 3,788,329, wherein the separate coiled wire conductors are wound in differing diameters separated from one another by tubular insulating sheaths and extend coaxially about a central lumen for receiving the stiffening stylet. Other lead body configurations involving use of stranded wire conductors also are formed with a stylet lumen. Most current cardiac leads employ multi-filar, parallel-wound, coiled wire conductors electrically connected in common in an electrically redundant fashion as a single polarity lead conductor in each of the unipolar, bipolar and multi-polar lead configurations. Such redundant coiled wire conductors of bipolar and multi-polar lead bodies are coaxially arranged about the stiffening stylet receiving lumen and insulated from one another by coaxially arranged insulating sheaths separating each coiled wire conductor from the adjacent coiled wire conductor(s). The stiffening stylet is advanced through a proximal connector pin opening into the lead body lumen to stiffen the lead body during the transvenous introduction.
The stiffening stylet is typically provided with an enlarged diameter stylet knob or handle that can be grasped and rotated to impart torque to the lead distal end to steer the lead distal end around turns in the transvenous pathway. A variety of other torque tools for imparting torque to a stylet alone or to the stylet and lead body are disclosed in U.S. Pat. Nos. 6,033,414, 6,132,390, 4,624,266 and 4,422,460.
Frequently, two or more cardiac leads are introduced transvenously through the venous system into the right heart chambers or coronary sinus of the heart during initial implantation or in the replacement of previously implanted cardiac leads. Atrial and ventricular pacing leads have long been implanted to locate atrial pace/sense electrode(s) in the right atrium (RA) and ventricular pacing leads in the right ventricle (RV). Typically, the ventricular lead body is straight so that the ventricular pace/sense electrode can be directed from the superior vena cava (SVC) through the tricuspid valve and into the RV appendage employing a stiffening stylet. The atrial lead body is formed to assume a J-shape so that the atrial pace/sense electrode is directed toward and into the RA appendage upon entry into the RA from the SVC. The J-shape is straightened for advancement through the transvenous path using a straight stiffening stylet or by confining the RA lead body in a guide catheter sheath.
Many approaches have been explored to simplify and facilitate implantation of the atrial and ventricular leads simultaneously. One approach disclosed in U.S. Pat. No. 4,602,645 includes a bilumen guide catheter having RA and RV lead delivery lumens disposed side-by-side and extending between RA and RV lead delivery lumen entry and exit ports. The RA lead delivery lumen exit port is located proximally to the RV lead delivery lumen exit port to facilitate the introduction of the RA lead and the assumption of the J-shape as the RA lead is advanced into the RA from the RA delivery lumen exit port. The RV lead delivery lumen is larger in diameter or the same diameter as the RA lead delivery lumen, depending on the diameters of the RA and RV lead bodies.
Moreover, a number of multi-polar, cardiac leads have been designed to accommodate more than two electrodes or to make electrical connection with other components, e.g., blood pressure sensors, temperature sensors, pH sensors, or the like, in the distal portion of the lead. The increased number of separate polarity coiled wire conductors is difficult to accommodate in the conventional coaxial coiled wire conductor winding arrangement employing tubular insulating sheaths to separate the coil wire conductors of differing diameters having a desired overall lead body outer diameter. It has long been desired to minimize the diameter of the transvenous cardiac lead body in order to facilitate the introduction of several cardiac leads from the IPG through the same transvenous pathway.
The complexity of the leads, the number of leads implanted in a common path, and the advancement of coronary sinus leads deep in a coronary vein have led to efforts to at least not increase and optimally to decrease the overall diameter of the cardiac lead body without sacrificing reliability and usability. More recently, it has been proposed to diminish the lead body further by eliminating the lumen for receiving the stiffening stylet and by reducing the gauge and coil diameter of the coiled wire conductor or replacing it with highly conductive stranded filament wires or cables. In bipolar or multi-polar leads, each such cable extends through a separate lumen of the lead body to maintain electrical isolation.
Over the last 30 years, it has become possible to reduce endocardial lead body diameters from 10 to 12 French (3.3 to 4.0 mm) down to 2 French (0.66 mm) presently through a variety of improvements in conductor and insulator materials and manufacturing techniques. The lead bodies of such small diameter, 2 French, endocardial leads must possess little if any column strength that could cause the lead distal end fixation mechanism and electrode to perforate through the myocardium during implantation and if the lead body were to become axially force-loaded during chronic implantation. As a result, the small diameter lead bodies lack “pushability”, that is the ability to advance the lead distal end axially when the lead proximal end is pushed axially, particularly when the lead body extends through the tortuous transvenous pathway.
Such small diameter endocardial leads then require distal fixation to maintain the electrode(s) at the desired implantation site. Active fixation helices that extend axially in alignment with the lead body to a sharpened distal tip and that have a helix diameter substantially equal to the lead body diameter are preferred because the fixation mechanism does not necessarily increase the overall diameter of the endocardial lead and is relatively robust, once the helix is screwed into the myocardium. Typically, but not necessarily, the fixation helix is electrically connected to a lead conductor and functions as a pace/sense electrode. In some cases, the lead body encloses one or more helical coiled or stranded wire conductor and lacks a lumen.
The lead bodies of such small diameter endocardial screw-in leads are so supple and flexible that it is difficult to rotate the lead distal end by application of rotary torque to the lead proximal end unless the lead body remains relatively straight and not confined by contact with vessel walls. This diminished “torqueability” prevents the rotation of the fixation helix at the lead distal end or renders the rotation unreliable once the lead body is advanced through a tortuous pathway and confined by contact against the vessel walls. To the degree that rotation torque can be transmitted from the lead proximal end to the lead distal end, the active fixation helix at the lead distal end can be over-rotated and screwed through the myocardium or under-rotated and not screwed into the myocardium sufficiently. Thus, it has been found necessary to use implantation instruments or tools that compensate for the lack of pushability and torqueability of the lead body.
In one approach, the lead body is enclosed within the lumen of a further sheath or introducer, and the lead and introducer are disposed within the lumen of the guide catheter. The fixation helix is located within the catheter lumen during advancement of the lead distal end fixation helix through the transvenous pathway and heart chamber or coronary vessel to dispose the fixation helix near the implantation site.
In commonly assigned U.S. Pat. No. 5,246,014, the introducer distal end and the lead distal end are configured to interlock or engage one another. The catheter, introducer and sheath lead body are advanced together through the transvenous, tortuous pathway to locate the fixation helix near the implantation site in the right atrium, right ventricle, coronary sinus, or cardiac vein. The fixation helix is pushed out of the catheter lumen distal end and the introducer catheter is rotated to screw the fixation helix into the myocardium by pushing and rotating the introducer proximal end extending proximally out of the catheter lumen outside the patient's body. In this approach, the inner introducer extends, in use, all the way to the catheter body distal end. Thus, the catheter distal segment is stiffened and may be difficult to advance through the tortuous pathway. Certain embodiments of the interlocking mechanism also increase the diameter of the lead distal end.
In further commonly assigned U.S. Pat. No. 6,408,214, the inner introducer, referred to as an inner sheath, and the outer catheter, referred to as an outer sheath each have preformed curves formed in distal sheath segments so that multiple curves can be induced as the inner and outer sheaths are axially adjusted relative to one another. The materials and dimensions of the inner and outer sheaths are selected to provide pushability and torqueablity of the assembly with the small diameter lead body disposed in the inner sheath lumen. The inner sheath is longer than the outer sheath, so that the inner sheath can be selectively moved out of the outer sheath lumen to advance a distal tip of the inner sheath to the implantation site. Again, the fixation helix is pushed out of the catheter lumen distal end and then rotated to screw the fixation helix into the myocardium by pushing and rotating the introducer proximal end extending proximally out of the catheter lumen outside the patient's body.
A further technique of implantation of such miniaturized endocardial screw-in leads disclosed in commonly assigned U.S. Pat. No. 5,897,584 employs a flexible guide catheter having a catheter body that has sufficient pushability and resistance to kinking that the guide catheter can be advanced through the transvenous pathway. The lead body is inserted into a catheter lumen during advancement of the catheter body distal end and fixation helix to the implantation site. Then, it is necessary to rotate the fixation helix from the proximal end of the assembly to screw the fixation helix into the myocardium at the implantation site. The distal advancement and rotation of the fixation helix is facilitated by a torque transfer device that is temporarily fitted over a proximal segment of the lead body extending proximally outside of the guide catheter hub and at a distance therefrom corresponding to or a fraction of the distance that the fixation helix is to be advanced distally for rotation into the myocardium.
Commonly assigned U.S. Pat. Nos. 6,280,433 and 6,379,346 disclose steerable catheters that are employed to access a blood vessel through a percutaneous incision and to be advanced to a site within the vascular system or a heart chamber. A bilumen catheter body is disclosed that includes a relatively large diameter delivery lumen and a smaller diameter stylet lumen that is blocked at a distal. The deflection mechanism in this case includes a stiffening stylet that can be selectively introduced into and removed from the stylet lumen from a proximal hub or handle. The stiffening stylet is advanced distally until the stylet distal end abuts the closed stylet lumen distal end to stiffen the catheter body to aid its introduction and advancement. The stylet distal end can be shaped when outside the stylet lumen opening to impart a curve to the catheter body when inserted into the lumen to assist in steering the catheter body distal end through the pathway. The stylet lumen is preferably lined with a wire coil sheath, and the handle and delivery lumen are preferably slittable by a slitting tool to aid in removing the introducer catheter from an electrical medical lead introduced through the delivery lumen. The delivery lumen exit port and the closed end of the stylet lumen are both located at the bilumen catheter body distal end.
A still further technique of implantation of such miniaturized, highly flexible, endocardial screw-in leads involves the use of a guidewire that is first advanced through the tortuous transvenous pathway. The endocardial lead is then advanced through the pathway alongside or over the guidewire as disclosed in U.S. Pat. Nos. 5,003,990, 5,304,218, 5,902,331, 6,132,456, and 6,185,464, for example. Some of these techniques require that the lead body be configured to provide an over-the-wire connection and possess sufficient column strength to be advanced over the guidewire. Other techniques employ elongated pusher tools that have sufficient column strength applied against the lead body distal end and extending alongside the lead body and the over the guidewire. These techniques are relatively complex to execute. Moreover, the rotation of the active fixation helix at the lead distal end through rotation of the assembly can still be problematic.
Thus, a need remains for an introducer system for a small diameter cardiac lead lacking pushability and torqueability that enables advancement of the distal electrode through tortuous pathways into a wide variety of implantation sites in a heart chamber or in a coronary vessel of the left heart chambers and reliable fixation at the selected implantation site.
Preferably, such a lead introducer system would also be of use in accessing cardiac sites for introducing medical instruments and materials or for implanting small diameter leads through other tortuous pathways of the body.